Feline allergen Fel d 4 (Fel d 4)

Fel d 4 is a major feline allergen belonging to the lipocalin family of proteins, primarily produced in the submandibular salivary glands and deposited on cat fur through grooming. It is the second most prevalent cat allergen after Fel d 1, with over 60% of cat-allergic individuals showing sensitization to this specific protein. Structurally, Fel d 4 functions as a transport protein for small hydrophobic molecules, such as pheromones, which may play a role in chemical signaling between animals. In humans, Fel d 4 acts as a potent trigger for Type I hypersensitivity reactions, where it cross-links IgE antibodies on the surface of mast cells and basophils, leading to the release of inflammatory mediators. This process results in clinical symptoms ranging from allergic rhinitis and conjunctivitis to severe bronchial asthma. In the context of therapeutics, Fel d 4 is a primary component in allergen-specific immunotherapy (AIT) formulations and is a critical target for component-resolved diagnostics (CRD) to differentiate between primary cat sensitization and cross-reactivity with other animal lipocalins.

Other names

Major cat allergen Fel d 4Felis domesticus allergen 4Lipocalin allergen Fel d 4Salivary lipocalin

Allergen immunotherapy (AIT) involves the administration of gradually increasing doses of the allergen to induce peripheral T-cell tolerance, increase regulatory T-cells (Tregs), and shift the immune response from a Th2 to a Th1 profile, thereby reducing IgE-mediated mast cell degranulation.